Purpose: The objective of this in vitro study was to evaluate the effect of thermocycling on retentive forces of different esthetic thermoplastic partial denture clasp materials including, poly¬oxymethylene (Acetal), polyetheretherketon (PEEK) and monomer free semi-rigid microcrystal¬line polymer (karadent). Material and methods: 2 Testing models with 2 natural premolar teeth used to test the retentive force of three types of esthetic thermoplastic clasps (N=6) Acetal, PEEK and karadent. After Thermo-cycling, the retention force of the clasps was measured at the same cross head speed. The data were collected, tabulated and a statistically analyzed using SPSS v26 , Kruskal Wallis was used for comparing quantitative non-parametric data of more than two different groups, followed by post-hoc Dunkan’s while Wilcoxon signed rank was used to compare quantitative non-parametric data of two related groups. Results: PEEK group has recorded a high statistically significant difference in retention force mean values prior to thermo-cycling, P-value ≤0.001. Following thermo-cycling, reduced retention force mean values were found for all groups with non-significant difference between the groups and a significant difference within each group. For the percentage of changes, there was a significant difference between the groups with the least percentage of changes in the Acetal clasp group. p ≤ 0.05. Conclusion: Within the limitations of this study, it was found that the thermoplastic resin clasps-showed a decreased retention values when exposed to thermo- cycling (2000 cycle) between (5 C-55 C) 30 seconds with significantly lower percentage of change for the Acetal than Peek and karadent esthetic clasp materials.